Pump

ABSTRACT

A pump for use in low-profile applications comprises a barrel for holding fluid; and a piston that converts a rotational driving force into a longitudinal driving motion within the barrel. The pump provides space saving advantages by reducing the need for external equipment and mechanisms around the pump for providing actuation or moving the actuating mechanism.

The present invention relates to pumps and how to provide a low-profilepump for dispensing small amounts of fluid.

Syringe pumps provide a mechanism for controlling the motion of thepiston within the barrel and therefore the displacement of fluid in thesyringe. The syringe used by the pump may be an integral part of thepump itself, or can commonly be a disposable part that can be used andreplaced, and may be a syringe that can also be used manually. A syringepump theoretically allows for a straightforward determination of theamount of fluid pumped, based on the distance moved by the piston withinthe barrel.

Conventional syringes and syringe pumps operate by the motion of aplunger displacing fluid within a barrel. When the plunger is advancedfrom an end within the barrel, fluid in the barrel is forced out theother end. On the other hand, when the plunger is drawn out of thebarrel through one end, fluid is drawn into the barrel through the otherend. To allow the pumping operation to occur properly, the plunger issealed against the barrel, so that fluid cannot pass around the plungerfor example.

The syringe pump can include an actuator attached to the end of thepiston plunger in order to push and/or pull the plunger in/out of thesyringe barrel. In such cases, it is necessary for the actuator to movewith the piston, and therefore space has to be provided for this.Further, a driving mechanism for moving the actuator needs to beprovided. As a result, the syringe pump often requires much more spacethan the syringe which it drives. For example, the overall length/heightof a syringe pump can include the length of the syringe, the length ofthe actuator and the length of the driving mechanism.

Other syringe pumps do not directly connect an actuator to the syringeplunger. Instead, the actuator may be driven to contact and push the endof a syringe plunger without becoming connected to the syringe. Thisallows for the syringe to be emptied by the pump, but not filled. Insuch cases, the syringes may be replaced when emptied or manuallyre-filled. Another problem with such pumps is that the user cannotalways be certain if the pump is dispensing fluid when the actuator isdisplaced, because the actuator may not be in contact with the syringeplunger when the actuator is first moved.

Conventional syringe pumps also suffer from a problem related to theseal formed by the syringe plunger with the syringe barrel.

One common method of sealing the plunger against the barrel indisposable syringes is by using an elastic seal such as an O-ring. Suchan O-ring is provided around the outside of the plunger, close to theend of the plunger driving fluid within the barrel. The O-ring providesa relatively deformable surface that can thus shape itself to the barreland form a tight seal. As such, the O-ring is positioned between heplunger and the barrel and so is in contact with the fluid in thebarrel.

Another method of sealing the plunger against the barrel is for thewhole plunger head to be made of an elastic material, so that theplunger head deforms as a whole to produce a seal within the barrel.

In both of these cases, the fluid in the barrel is in contact with theelastic material that is being used to create the seal. This raisespossible fluid contamination/interaction issues. In fluidic andmicrofluidic applications, and biological fluidic applications inparticular, it is undesirable to introduce materials into the systemwhich might somehow react with the fluids or leach contaminants into theprocess fluids and somehow affect the experiment being performed in anunexpected and/or unquantifiable manner.

Further, the use of an elastic sealing material causes a characteristicstick/slip jump when first moving the plunger. This is caused due tohigh static friction between the elastic sealing material and barrel,which must be overcome to start the plunger moving. The high staticfriction means a correspondingly large force is required to start movingthe plunger, and a characteristic jerk occurs before smooth plungermotion can be observed once enough force has been applied to the plungerto overcome the static friction. Even after the static friction has beenovercome, the presence of the elastic O-ring results in a relativelylarge amount of dynamic friction (and hence a corresponding largerequired driving force) that must be overcome to keep the plungermoving. This makes fine control of the syringe difficult, especiallywhen first beginning to move the plunger.

Further, it is typical for conventional syringes and syringe pumps tosomewhat rely upon deformation of the outer barrel around the pistonseal (be it an O-ring or the entire piston head) to achieve a good seal.That is, the barrel will deform slightly outwards in the region of theseal to allow the piston to be moved whilst maintaining pressure on theseal.

An alternative to the elastic material approach is to make the syringe(from metal for example) so the piston is an exact fit for the barrel.However, this approach is expensive and is therefore not well suited tothe mass manufacture of disposable syringes. The use of metal may alsointroduce fluid contamination considerations.

The present invention aims to provide a syringe pump that at leastpartly overcomes some or all of the forgoing problems.

According to an aspect of the invention, there is provided a pumpcomprising: a barrel for holding fluid; and a piston for drawing fluidinto the barrel and driving fluid out of the barrel, wherein the pistoncomprises a plunger configured to move within the barrel and a sheathconfigured to move around an outer surface of the barrel; wherein aninner surface of the sheath and the outer surface of the barrel havecomplementary screw threads so that, in use, rotating the piston causesthe piston to travel along the barrel. That is, rotating the pistoncauses the plunger and sheath to travel along the barrel.

According to this aspect, a pump having a piston that translates arotational actuation force into a longitudinal pumping motion isprovided. This avoids the need to provide any extra hardware ormechanisms to linearly actuate the pump, because the piston provides therotational/linear movement conversion. Further, by providing a screwthread outside the pump barrel, rather than inside, the screw threaddoes not interfere with the operation of the pump itself. That is, thescrew thread does not compromise the seal between the piston and thebarrel, and it does not cause any loss of stroke-volume that might beencountered if the thread was placed on the inside of the barrel. As aresult, the pump is more suitable for use in applications wherespace-saving is an important consideration. The pump is also suitablefor applications requiring fine control of flow rates or pumped amounts.This is because the screw thread linking the barrel and the piston canbe formed with whatever pitch is appropriate to the application.Changing the pitch of the screw thread changes the number of turnsrequired to move the piston a particular longitudinal distance.Therefore, the pitch can be changed to provide very fine control, forexample, by requiring many turns to move the piston a short longitudinaldistance.

The pump can further comprise a piston head for forming a seal againstan inner surface of the barrel, wherein the piston head is connected tothe plunger of the piston so that the piston head is free to rotate withrespect to the plunger or the barrel. In some situations, for example,this allows the piston head to move longitudinally within the barrelwithout needing to rotate with respect to the barrel. That is, thepiston head can be rotationally stationary with respect to the barrelwhilst rotating with respect to the piston and plunger. In general, theprovision of another possible point of rotation (i.e. between the pistonhead and the plunger) allows for the piston head to slip against thesurface of least resistance—be that the surface of the barrel or thesurface of the plunger. As such, the piston head will slide against thesurface of least resistance and therefore minimise the rotationalfrictional load, thereby reducing the driving force required to move thepiston.

The pump can be configured to resist rotation of piston relative thebarrel at a predetermined position. The sheath can be provided with alug for resisting rotation of the piston relative to the barrel when thelug is brought into contact with another portion of the pump. Thisprovides a hard stop for the piston, for example close to (or at) thepoint the piston head reaches the end of the barrel, without jamming thescrew mechanism between the piston and the barrel. It also provides amechanism for aligning the pump piston with respect to the barrel, whichcan be useful when configuring the pump for engagement with an actuatingmember. It also enables a known position of the piston to be determinedwithin the plunger, if for some reason the position becomes unknown(e.g. if a position tracking system fails).

The plunger can be hollow. The piston can comprise, an engagementsection for engaging with a driving member and enabling the driver toturn the piston. The engagement section can comprise an opening into thehollow plunger. This allows for an actuating member, that engages withthe engagement section to be received inside the hollow plunger. This inturn allows for longitudinal motion of the piston relative to theactuating member, and so avoids the need to provide any mechanism tolongitudinally move the actuating member as the piston is moved.Instead, the piston can move around the actuating member itself.

The engagement section can comprise a slot for engaging a driving memberby relative motion between the pump and the driving member in adirection substantially perpendicular to the direction of travel of thepiston along the barrel. This allows the pump to be used in situationsin which space in the longitudinal/pumping direction is limited, or forexample where the driving member is fixed in position. The pump can bebrought into engagement with the actuating member in a directionsubstantially perpendicular to the pumping direction, and no furtherlinkage is required to connect the pump to the actuating mechanism. Thisavoids the need for a loading/engagement mechanism requiringlongitudinal motion and therefore reduces the longitudinal space neededfor engagement. This also allows for an analysis apparatus comprising abody and a cartridge attachable to the body, wherein the cartridgecomprises the pump and wherein the body comprises a driving member forengaging with the pump by relative motion between the pump and thedriving member in a direction substantially perpendicular to thedirection of travel of the piston along the barrel.

The pump can further comprise the driving member. The driving member canhave two flat and substantially parallel sides for engaging theengagement section. This allows for the engagement section to slide onand off the driving member easily, and simultaneously provides drivingsurfaces for transmitting the rotational actuation from actuating memberto the piston.

The pump can be configured such that, in use, the driving member extendswithin the hollow plunger as the piston travels along the barrel. Thedriving member, in use, can move rotationally with respect to the barrelto drive the piston within the barrel. The pump can further comprise aworm gear arranged to rotate the driving member, the worm gear beingarranged to rotate with an axis of rotation substantially perpendicularto the axis of rotation of the driving member. According to thisconstruction, a motor for driving the piston, via the worm gear, can bearranged with its rotor having a rotational axis substantiallyperpendicularly to the rotational axis of the piston. Since motors aretypically longer along their rotational axis than across their width,this allows a space saving pump arrangement which reduces the spaceneeded along the rotational axis of the piston.

In an alternative arrangement, the pump can comprise a driving memberthat engages the outer surface of the piston. This configuration canmaintain the space saving advantages whilst allowing the driving memberto be thicker than the piston, because the driving member is notrestricted by the need to fit within the piston.

According to another aspect, there is provided a system comprising, acasing; a pump comprising a barrel and a piston; and an actuator formoving the piston relative to the barrel; wherein the pump and actuatorare provided within the casing; and wherein the system is configured tohold the actuator translationally stationary with respect to the casingwhilst the piston is moved relative to the barrel.

According to another aspect, there is provided a system comprising, apump comprising a barrel and a piston; and an actuator for moving thepiston relative to the barrel; wherein the system is configured to holdthe actuator translationally stationary with respect to the piston andthe barrel whilst the piston is moved relative to the barrel.

According to this aspect, because it is not necessary to move theactuator in a translational sense, the height and therefore volume ofthe system can be reduced compared to a system that must leave space forthe actuator to move within the case.

The system can be configured to hold the barrel translationallystationary with respect to the casing whilst the piston is movedrelative to the barrel. In this case, the piston can move in atranslational sense within the casing, during a pumping operation,whilst the other components are not moved in a translational sense. Thisallows the barrel to be easily connected to a fluidic system, forexample, without the need to allow for motion of the barrel with respectto the fluidics. The actuator can be rotatable with respect to thecasing, to allow driving of pump via a rotational mechanism. The barreland/or the piston can comprise or consist of a plastics material. Thebarrel can comprise or consist of acrylonitrile butadiene styrene,polycarbonate, polytetrafluoroethylene, ultra-high-molecular-weightpolyethylene, polypropylene, perfluoroalkoxy, poly(methyl methacrylate)or fluorinated ethylene propylene. The piston can comprise acetal and/orpolybutylene terephthalate, and can further comprise glass fibre and/orpolytetrafluoroethylene. The materials for both the barrel and thepiston are preferably easily moulded, and provide good structuralrigidity. The material of the barrel, which is in contact with thefluids entering and exiting the pump, preferably exhibits low bindingwith the fluids being processed, and low leaching of contaminants intothe fluids. This is particularly important in biological applications,such as biological nanopore applications, in which contaminants couldblock pores or otherwise interact with and/or deactivate biologicalmolecules in unexpected and undesirable ways.

According to another aspect, the invention provides a method of pumpingfluid, the method comprising: providing a barrel for holding fluid;providing a piston for drawing fluid into the barrel and driving fluidout of the barrel, wherein the piston comprises a plunger configured tomove within the barrel and a sheath configured to move around an outersurface of the barrel; and rotating the piston relative the barrel,along complementary screw threads provided on an inner surface of thesheath and the outer surface of the barrel, so that the piston travelsalong the barrel.

The method can further comprise providing the driving force for rotatingthe piston via a motor, wherein an output shaft of the motor has arotational axis substantially perpendicular to the rotational axis ofthe piston.

The present invention will be described with reference to exemplaryembodiments and the accompanying Figures in which:

FIG. 1 a and FIG. 1 b are perspective views of a syringe pump system,with the syringe pump advanced and withdrawn respectively;

FIG. 2 a and FIG. 2 b are perspective views of the syringe pump andactuator of FIGS. 1 a and 1 b, with the syringe pump advanced andwithdrawn respectively;

FIG. 3 a and FIG. 3 b are perspective views of the syringe pump of FIGS.1 a and 1 b, with the syringe pump advanced and withdrawn respectively;

FIG. 4 a is a side elevation view of the syringe pump system as show inFIG. 1 a, and FIG. 4 b is plan view of the system of FIG. 4 a throughthe plane D-D;

FIG. 5 a and FIG. 5 b are sectional views of the syringe pump of FIGS. 3a and 3 b, with the syringe pump advanced and withdrawn respectively;

FIG. 6 is schematic diagram of the plunger head of the syringe pump ofFIG. 5;

FIG. 7 is a cross-sectional view of the plunger head of FIG. 6;

FIG. 8 is a perspective view of the plunger head of FIG. 6; and

FIG. 9 is a perspective view of a cartridge for use with an analysisunit.

The present invention has identified that conventional syringe pumps areunsuitable for many fluidic and microfluidic applications. For example,WO 2009/077734 hereby incorporated by reference, relates to theformation of layers of amphiphilic molecules, in which nanopores can bedeployed to provide an environment which can be useful, for example, forsequencing polynucleotides. This is an example of a ‘nanoporeapplication’, referred to below. The formation of the bi-layer, theprovision of the nanopores, and the subsequent provision of test fluidsrequire careful control of the fluidic environment, both in mechanicaland chemical terms. In the case of pumping lipid to form bi-layers, anextremely slow pumping speed is required. An example range is between 1μl/s to 0.1 μl/s. The stick/slip issues with conventionalelastic-sealing syringe pumps makes control of such flow rates extremelyproblematic, and can make repeatability of experiments very difficult.This is particularly relevant when considering the small volumes ofliquids being displaced and the need to ensure that accurate amounts ofa required fluid are provided at the correct time.

Another consideration for nanopore applications is that the presence ofcontaminants in the system poses a risk of blocking of the nanoporesand/or interacting with biological molecules (including the biologicalnanopores) in an undesirable way. As such, it is desirable to minimisethe number of materials in contact with the process fluids and, forthose materials that will contact the process fluids, use materials thatwill have the minimum interaction with the fluids (e.g. exhibiting lowbinding with the fluids, low leaching of contaminants into the fluids).Contamination is a particular problem with biological nanopores as thepore may be temporarily or permanently deactivated. Also, other proteinsin the system may be deactivated or denatured.

In addition to these considerations, the invention identifies a need toprovide a pump that makes the best use of the available space. Forexample, WO 2011067559, hereby incorporated by reference, discloses abiochemical analysis instrument that utilises nanopores deployed in alipid bi-layer to, for example, sequence polynucleotides. As mentionedabove, the formation of the bi-layer and the provision of the nanoporesrequire careful control of the microfluidic environment but at the sametime the space available for the fluidics is limited.

Of course, many of the above considerations are not limited to nanoporeapplications, and are generally applicable to other fluidic andmicrofluidic environments.

FIG. 1 shows a syringe pump system 1, which incorporates a syringe pumpthat comprises a piston 20 and a barrel 30, an actuation system 40, amotor 60 and a worm gear 50. The motor 60 drives the worm gear 50, whichin turn drives the actuation system, which in turn drives the syringepump. As the syringe pump is driven, the piston 20 moves with respect tothe barrel 30. FIG. 1 a shows the piston 20 advanced within the barrel30, whilst FIG. 1 b shows the piston 20 relatively withdrawn within thebarrel 30.

FIGS. 2 a and 2 b correspond to the configurations of FIGS. 1 a and 1 brespectively, omitting the motor 60 and worm gear 50 and only showingthe driving member 41 of the actuation system 40. Similarly, FIGS. 3 aand 3 b correspond to the configurations of FIGS. 2 a and 2 b but omitthe driving member 41. FIGS. 5 a and 5 b show cross-section viewsthrough the pump and driving member 41 as pictured in FIGS. 2 a and 2 brespectively.

FIG. 4 a shows a side view of the pump system 1 of FIG. 1. FIG. 4 bshows a cross-section view through the plane D-D as indicated in FIG. 4a.

Pumping operation of the pump assembly 1 is achieved by the motion ofpiston 20 driving a barrier surface/piston head 10 (discussed below) anddisplacing fluid within the barrel 30 in the manner of a syringe. Thepiston head 10 is circular in cross-section and fits snugly within thecylindrical barrel 30 so that, when the plunger 21 is advanced withinthe barrel 30 (i.e. moved downwards in the geometry of FIGS. 1-3) fluidin the barrel 30 is forced through an opening 31 in the barrel 30. Onthe other hand, when the plunger 21 is drawn out of the barrel 30, fluidis drawn in to the barrel 30 through the opening 31. In FIG. 5 theopening 31 in the barrel is shown as an orifice in the end of the barrel30, but in alternative constructions it can be a different shape orsize.

As can be seen from FIGS. 1-4, the pump consists of a barrel section 30for holding fluid and a piston section 20 for drawing fluid into thebarrel 30 and driving fluid out of the barrel 30. For fluidics ornanopore applications, the pump may be operable to produce a variety offlow rates. For example, in nanopore applications, it may be desirablefor a pump to produce flow rates of from 50 to 100 μl/s for cleaning;for initially priming the fluid lines with the working fluid it may bedesirable for a pump to produce flow rates of from 20 to 50 μl/s; forproviding lipid for bi-layer formation it may be desirable for a pump toproduce flow rates of from 0.1 to 0.5 μl/s; and for providing pores orbuffer it may be desirable for a pump to produce flow rates of 1 to 3μl/s. A single pump may be capable of producing the flow rates for eachof these requirements, but individual pumps for each requirement mayalso be used. In general, it is desirable for the pump to produce flowrates of 0.01 μl/s or more, optionally 0.05 μl/s or more, furtheroptionally 0.1 μl/s or more, still further optionally 20 μl/s or moreand still further optionally 50 μl/s or more. Further it may bedesirable for the pump to be operable to produce flow rates of 500 μl/sor less, optionally 200 μl/s or less, further optionally 100 μl/s orless, still further optionally 50 μl/s/ and still further optionally 20μl/s or less.

The piston 20 comprises a plunger section 21 and a sheath section 22.The plunger 21 is configured to move within the barrel 30 and displacethe piston head 10, whilst the sheath is configured to move around theouter surface of the barrel 30. That is, the barrel 30 fits between theplunger 21 and the sheath 22. The plunger 21 and the sheath 22 areconnected to each other and are preferably formed together, for examplevia moulding.

This piston section 20 does not come into contact with the fluid in thebarrel 30. This is because the piston head 10 is provided at the end ofplunger 21. As discussed in more detail below, with reference to FIGS.6-8, the piston head 10 provides a barrier surface which seals acrossthe barrel 30, and so the piston 20 is isolated from the fluid.

The barrel 30 and the sheath 22 are constructed to screw together. Assuch, the inner surface of the sheath 22 and the outer surface of thebarrel have complementary screw threads so that the piston 20 willtravel along the barrel 30 as the piston 20 is rotated. Further, thescrew thread prevents the piston 20 being moved with respect to thebarrel 30 by a force applied in the direction of piston travel in thebarrel 30.

That is, a rotational driving motion is needed to produce a linearmotion of the piston 20 with respect to the barrel 30. This rotationalactuation, converting the rotational movement to a linear movement viathe thread, allows fine control of the movement of the piston 20, bysuitable selection of the thread pitch. That is, because a 360°rotational movement is required to move the piston 20 longitudinally byone thread pitch, the thread pitch can be selected as required to givethe descried level of control over the piston 20 displacement. Inpreferred embodiments, the thread can be pitched to provide 10 mm orless of longitudinal motion per revolution of the piston, optionally 5mm or less per revolution, further optionally 2 mm or less perrevolution and still further optionally 1 mm or less per revolution. Inaddition, the selection of barrel volume and gearing ratios in theactuation system further contribute to controlling the flow ratesproduced by the pump. The provision of the screw thread on the externalsurface of the barrel 30 is also advantageous. If the screw thread wereprovided on the inner surface of the barrel 30, it could potentiallyinterfere with the sealing of the piston head 10 against the barrel 30.Alternatively, to avoid such interference, the length of the barrelwould need to be extended to allow for the provision of a screw-sectionthat does not overlap with stroked-volume of the barrel 30. However,this would result in a larger and more unwieldy pump, and would not besuitable for use in applications with limited space.

Preferably, the screw connection, between the barrel 30 and the piston20, also keeps the piston 20 held rigidly in position with respect tothe barrel via the thread. This is advantageous because it helps avoidvariation in forces acting between the barrel 30 and the piston 20 thatcould be introduced if the angle of the piston 20 within the barrel 30was able to vary, which in turn could cause unwanted forces acting onthe pump and/or lead to uncertainty in the position of the piston 20within the barrel 30. That is, flexibility in the angle of the piston 20within the barrel 30 would mean that force could be applied into thebarrel wall through the piston head and/or, for a given movement of thedriving rod 41, the position of the piston 30 would not be accuratelyknown.

The rigidity of the piston 20 with respect to its position in the barrel30 can also be assisted by suitable material selection for the piston.This can also assist in ensuring the piston head 10 is held firmly inposition. In addition, because having a thread interface introduces anefficiency loss into the pump driving system (because of the additionalfriction between the piston 20 and the barrel 30, compared with aconventional sliding syringe pump), material selection can help providelubrication. Because (as mentioned above) neither the piston plunger 21nor the piston sheath 22 comes into direct contact with the fluid beingpumped, there is a low risk of the piston material causing anycontamination of the fluid being pumped. Therefore, materials for thepiston can be selected primarily based upon their mechanical properties.Preferably materials that could be used for the piston are acetal (i.e.polyoxymethylene or POM), or polybutylene terephthalate (PBT) with addedglass fibre and/or added lubricants such as PTFE. Examples of suchmaterials are HOSTAFORM® C9021 GV1/20 XGM and LUBRIONE® PS-30GF/15T/02S.

Since the barrel 30 comes into contact with the fluid being pumped, itis preferable to make the barrel material selection based upon thedesire to avoid introducing contaminants. For example, in nanoporeapplications the presence of contaminants in the system poses a risk ofblocking of the nanopores or possibly inactivating biological nanoporesor other biological molecules present in the fluids being processed. Assuch, it is desirable to minimise the number of materials in contactwith the process fluids and, for those materials that will contact theprocess fluids, use materials that will have the minimum interactionwith the fluids (e.g. exhibiting low binding with the fluids, and lowleaching of contaminants into the fluids). As a result, the plungerbarrel 30 is preferably made of a plastics material for ease ofmanufacture and cost effectiveness, and is more preferably an easilymouldable plastics material such as acrylonitrile butadiene styrene(ABS) polycarbonate (PC) or poly(methyl methacrylate) (PMMA). Otherpossible materials include polytetrafluoroethylene,ultra-high-molecular-weight polyethylene, polypropylene, perfluoroalkoxyor fluorinated ethylene propylene.

For a fluidics or nanopore application, the barrel can have a volume of10 ml or less, optionally 5 ml or less, further optionally 2 ml or less,and still further optionally 1 ml or less.

A preferable method of manufacturing the pump piston 20 and barrel 30 isby moulding, as this allows large scale manufacture with good mechanicalprecision at relatively low cost. To assist with moulding the threadedbarrel, the thread can have two flat surfaces removed, from two oppositesides of the thread. Then, when the component is moulded, the thread canbe formed via two tool halves rather than a single tool thread thatneeds to be unwound from the moulded product.

The piston 20 is provided with a lug 24. As can be seen in FIG. 2, thelug 24 is provided at the bottom of the piston 20, on the sheath 22, anda further lug 34 is provided in connection with the barrel 30. Movementof the piston 20 is limited by the lugs 24,34 because lug 24 projectslower than the base of the piston 20. Therefore, the lug 24 comes intocontact with the lug 34 when the piston 20 has been advanced into thebarrel 30 and the piston head 10 is close to, or at, the end of thebarrel 30. The point at which the lugs 24,34 contact each other definesthe limit that the piston 20 can be screwed onto the barrel 30, and sothe furthest point to which the piston 20 can be advanced. That is, thelugs 24,34 prevent the piston 20 being advanced any further, andtherefore avoid over-tightening or jamming of the screw mechanism. Thisalso allows easy initial manual positioning of the piston 20 (e.g.before engaging the pump barrel/piston assembly with the actuatingassembly 40) and, when the assembly 1 is actuated, gives a hard stop onthe angular position that actuation motor 60 can drive to.

As previously discussed, conventional syringe pumps commonly seal theplunger against the barrel with an elastomeric seal such as an O-ring.Such an O-ring is provided around the outside of plunger, and isconventionally in contact with the fluid in the barrel. When emptyingthe pump, the seal helps prevent fluid from flowing around the plungerrather than through the orifice in the barrel. When filling the pump bydrawing fluid through the orifice, the seal helps reduce air from thepump surroundings being drawn into the barrel around the plunger and soensures that fluid is drawn in through the orifice. The seal isconventionally at least partly maintained by the syringe barrel flexingaround the plunger and thus pushing inwardly onto the plunger as theplunger is moved through the barrel. However, the flexibility of thebarrel introduces an inherent lack of accuracy in the syringe design,because the volume of the barrel changes as the plunger is moved, andtherefore the volume of fluid expelled from (or drawn into) the barrelis not known accurately. Preferably the barrel is substantially rigid.

The piston head 10 is shown in detail in FIGS. 6 to 8. In contrast toconventional pistons, the piston head 10 has a piston seal that sealsagainst the barrel 30 differently.

In the Figures, the piston head 10 fits to the end of the plunger 21, aridge on an inner surface of the plunger clipping over the depression 17formed in the piston head. This construction is preferable, because thepiston head 10 can remain free to rotate with respect to the plunger 21and/or the barrel 30. This reduces friction within the pump as it isactuated, because piston head 10 only needs to rotate with respect tothe surface presenting the least resistance. That is, the piston head 10is free to rotate with respect to whichever of the plunger and thebarrel presents the least frictional resistance to rotation, and is notforced to rotate with respect to the higher friction element (whicheverit is). Of course, the skilled person will appreciated that the sameadvantage can be achieved by providing a depression on the inner surfaceof the hollow plunger 21 and a corresponding ridge on the body of thepiston head 10.

However, any suitable method of attaching the piston head 10 to aplunger 21 may be used. In some constructions, especially if friction isnot a particular concern, the piston head 10 might not be separate tothe plunger 21; that is, the piston head 10 can be formed integrallywith the body of the plunger 21 itself.

The piston head 10 has piston seal comprising a barrier portion 11 thatforms a barrier across the barrel 30. The barrier portion 11 has abarrier surface 12 that faces the fluid being displaced within thebarrel (whether that fluid is being driven out of the barrel 30 or drawninto the barrel 30).

The peripheral portion of the barrier portion 11 (that is, the radiallyoutermost portion) is formed into a lip 13, which projects from theopposite side of the barrier portion 11 to the barrier surface 12. Inthe figures, the lip 13 stands proud from the upper surface of thebarrier portion 11, projecting upwards whilst the barrier surface (whichcontacts the liquid in the syringe barrel) faces downwards. That is, thelip 13 is formed by the edge of the barrier portion 11 retreating backin the direction of the plunger 21 and away from the base 32 of thebarrel 30. As such, the lip 13 extends and projects at least partiallyaround resilient member 15 (discussed in more detail below). However,the lip 13 still at least partially extends outwards in a radialdirection from the centre of the pump head 10. As such, the barriersurface 12 has a slightly convex shape with respect to the barrelchamber 33 (i.e. a convex shape when the barrier surface 12 is vieweddirectly), especially in the vicinity of the inner surface 34 of thebarrel 30 and the point at which the lip 13 merges into the bulk of thebarrier portion 11.

The widest diameter of the piston seal occurs on the outer surface ofthe lip 13 (i.e. the continuation of the barrier surface 12). Forfluidics or nanopore applications, the widest outer diameter of thepiston seal may be 50 mm or less, optionally 25 mm or less, and stillfurther optionally 15 mm or less. In a preferred embodiment, the outerdiameter is 11.6 mm. Further, the outer diameter may be 1 mm or more,optionally 3 mm or more, further optionally 5 mm or more and stillfurther optionally 10 mm or more. At rest, when the piston head 10 isnot assembled into a corresponding barrel 30, this widest diameter ofthe pump seal is wider than the inner diameter of the barrel 30. Assuch, when the pump head 10 is inserted into the barrel 30, the lip 13is deflected inwardly (i.e. towards the centre of the pump head). Thatis, the pump head 10 deforms to allow insertion into the barrel 30.

The barrier portion 11 of the pump head 10 is preferably sufficientlyrigid, such that it will resist the deflection of the lip 13 and henceforce the lip 13 against the barrel 30 and form a seal around the pistonhead 10. The barrier portion may be made of plastic or a material otherthan plastic, such as a metal. However metals are generally tooinflexible to be suitable and are generally not preferred, unlessprovided for example as a thin layer or coating on the resilient member.Another reason plastics are preferred is because they are typicallycheaper than metals.

Another reason plastics might be preferred over metals would be if thereare concerns regarding metals reacting with or contaminating the fluidbeing pumped. For example, in lab-on-a-chip applications, such asnanopore applications, it is desirable to minimise fluid contaminationand so plastics materials are often more suitable for constructingfluidic and microfluidic circuits than metals. Similarly, to avoidcontamination when using plastics for the piston head 10 it ispreferable to use plastics which exhibit low chemical/plasticiserleaching. Preferable plastics include polytetrafluoroethylene (PTFE),ultra-high-molecular-weight polyethylene (UHMWPE), polypropylene (PP),high density polyethylene (HDPE), perfluoroalkoxy (PFA) or fluorinatedethylene propylene (FEP).

The use of substantially rigid material for the barrier portion 11circumvents the need for flexible barrel to help form the seal. Instead,the seal can be formed by the deflection of the barrier portion 11against the barrel 30. However, the use of rigid materials such asplastics for the barrier portion 11 has a potential drawback relating tothe durability of the seal. Over time, once the piston head 10 has beenpositioned in the barrel 30, the material of the barrier portion mightexhibit creep in the region of the lip 13. That is, the material mightbegin to deform to take the shape of the barrel 30, decreasing the forcepushing the lip 13 against the inner wall 34 of the barrel. As thisprocess occurs, the quality of the seal around the piston head 10 willdecrease.

The quality of the seal around the piston head 10 is particularlyimportant in lab-on-a-chip applications such as nanopore applications.This is because such applications operate with very small volumes offluid and so it is important that the amount of fluid being dispensed bya pump is dispensed as accurately as possible. The introduction of aweak seal in a pump reduces the accuracy of dispensing because fluid canleak around the plunger 21 instead of exiting the pump 1 through theorifice 31, without the operator's knowledge. As such, an experimentwould proceed with the operator assuming a certain amount of fluid hadbeen dispensed, when in fact a different amount had been dispensed.

Further, when charging the pump 1 by drawing fluid in through theorifice 31 a weak seal can cause a similar problem: instead of drawingin fluid, air from the pump surroundings can enter the barrel chamber 33around the plunger 21 instead of fluid being drawn into the chamber 33via the end of the barrel 31. Once again, the operator would not beaware of this, and so would assume a certain amount of fluid had beencharged to the pump 1, when in fact a lesser amount had been charged.

The pump 1 at least partially overcomes these problems by the provisionof a resilient member 15 behind the lip 13. That is, the resilientmember 15 is provided on the opposite side of the barrier portion 11 tothe barrier surface 12, and inside (i.e. closer to the centre of thepiston head 10) the lip 13. The lip 13 thus projects at least partiallyaround the resilient member 15. That is, as shown in the Figures, thelip 13 can extend around the resilient member 15, whilst part of theresilient member 15 can extend further away from the barrier portion 11than the lip 13, in the axial direction of the piston, along theretaining portion 16. Increasing the distance that the resilient portion15 extends along the retaining portion 16 increases the surface areaprovided between the two sections and thus increases the strength of anybond between the two sections.

The resilient member 15 can be an elastomeric material which resistscompression and therefore the deformation of lip 13 as the plunger 21 isinserted into the barrel 30. As such, even if the barrier portion 11and/or lip 13 is subject to material creep, the resilient member 15 willcontinue to resist its own compression and force the lip 13 back towardsthe inner wall 34 of the barrel 30. This maintains a good seal.

If the force resisting the deformation of the lip 13 is too strong, thepump 1 can become difficult to actuate. That is, if the lip 13 is pushedagainst the barrel 30 too strongly, it can become difficult to move theplunger 21 within the barrel, making the pump 1 stiff to operate. Toprevent the pump 1 becoming too stiff, the lip 13 can be reduced inthickness. Reducing the thickness of the lip 13 reduces the hoopstresses in the lip 13 as it is deformed, and hence reduces the forcewith which the lip 13 resists deformation.

However, reducing the lip 13 thickness has an associated potentialdisadvantage that an overly thin lip 13 could be easily damaged, duringeither operation or assembly for example. If a lip 13 is too thin, anydamage could lease to an incomplete seal being formed, and thus preventthe pump 1 working properly.

Therefore, rather than reducing the thickness of the entire lip 13uniformly, it can be preferable to shape the lip to be tapered so as tothin towards the outer end of the lip 13. That is, the thickness of thelip 13 can varied to be thinner at the tip of the lip 13 and thickerwhere the lip joins the barrier portion 11. The tapering constructionallows for a mechanically strong lip to be formed, which is resistant todamage and which also allows for a reduction in hoop stress in theregion of the lip 13 towards the tip that will be deformed when thepiston head 10 is inserted in the barrel 30.

The resilient member 15 can be elastic, such as a metal spring or anelastomeric material such as a silicone or a thermoplastic elastomer(TPE). One advantage of the construction of the piston head 10 is that,as long as the seal is functioning, the resilient member 15 does notcome into contact with the fluid being pumped in and out of the chamber33. As such, there is no direct contamination of the fluid by contactingthe resilient member 15. However, as discussed above the use of metalmay be undesirable in certain applications. Further, the use ofelastomeric materials, such as TPE, may be preferred to assist insimplifying the manufacture of the piston head 10. For example, two-shotmoulding could be used when employing an elastomeric resilient member.

Another advantage of the construction of the piston head 10 is that theresilient member does not come into contact with the inner surface 33 ofthe barrel 30. This is advantageous because it results in the contactbetween the plunger 21 and the barrel 30 occurring only around the lip13 of the piston head 10. Since both the barrel 30 and the lip13/barrier portion 11 are made of plastics materials the frictionbetween the surfaces will be relatively low, compared to a conventionsyringe plunger seal in which the contact (and seal) occurs between thebarrel and the elastic material of the sealing O-ring.

For example, Table 1 shows the dynamic coefficient of frictions for someplastics materials. In some cases, the coefficient of dynamic frictionof PTFE relative to steel, measured according to ASTM D1894 can be 0.05to 0.16. In some cases, the coefficient of dynamic friction ofpolypropylene relative to steel, measured according to ASTM D1894 can be0.2 to 0.4. In some cases, the coefficient of dynamic friction of ETFErelative to steel, measured according to ASTM D1894 can be 0.3 to 0.74.In some cases, the coefficient of dynamic friction of PMMA relative tosteel, measured according to ASTM D1894 can be 0.15 to 0.8. Preferablematerials for the barrier portion and the barrel have a coefficient ofdynamic friction relative to steel of 0.4 or less, preferably 0.2 orless, measured in accordance with ASTM D1894.

TABLE 1 Coefficients of dynamic friction of some materials Coefficientof Material Dynamic Friction UHMWPE 0.1-0.2 PTFE 0.05-.1  FEP 0.08-.3 Polypropylene 0.3-0.4 HDPE 0.07-0.4  Ethylene tetrafluoroethylene (ETFE)0.3-0.4 PMMA 0.5-0.8 Polycarbonate 0.3-0.9 Nylon 0.2-0.5 Acetal 0.1-0.4Acrylonitrile butadiene styrene (ABS) 0.2-0.5 NexPrene (RTM)thermoplastic vulcanizates 0.4-0.5

However, as can be seen from the table, plastics can have highercoefficients of friction. In particular, softer materials more commonlyused as seal materials are likely to have higher coefficient ofmaterials. For example, the coefficient of friction of silicone rubberis anecdotally close to 1, and special materials (such as NexPrene®listed in Table 1) have been developed to try and obtain similarclastomeric properties to silicone whilst exhibiting lower coefficientsof friction that silicone. However, as shown in Table 1, the coefficientof friction of materials such as NexPrene is not as low as materialssuch as PTFE or UHMWPE for example.

As a result, the piston seal of the invention can reduce occurrence ofstick-slip when the pump is driven by using materials to form the sealthat are not conventionally suitable. This is due to the differentconstruction of the seal, compared to conventional seals that provide aresilient or energised seal without bringing the material providingresilience into contact with the barrel. This results in both a smootherpumping operation and also, a lower driving force being required toactuate the pump. This in turn results in lower pressures in the pumpchamber 33 and so smaller amounts of air compression and more accuratedispensing.

Another way of lowering the friction between the piston and the barrelis to provide a suitable surface treatment on either the barrel or thepiston, or both. The surface treatment can introduce a texture thatreduces the overall area of contact between the piston and the barrel,and thus the friction acting between those surfaces. On the other hand,the surface is preferably not textured so much as to compromise thequality of the seal. As such, the ideal surface finish may be materialdependent. However, for example, a sparked surface finish of 30 VDI(according to the Verein Deutscher Ingenieure 3400 Guideline, equivalentto an arithmetic mean roughness value, R_(a), of 3.2 μm) of on theplunger seal surface/lip 13 and a polished barrel surface can beeffective, particularly on a polycarbonate barrel for example. Moregenerally a sparked surface finish of 18 VDI (R_(a) 0.8 μm) to 39 VDI(R_(a) 9 μm) may be effective on the plunger seal surface/lip 13.

As such, the piston head 10 provides a strong lasting seal by theprovision of the resilient member 15 behind the lip 13, whilst alsoavoiding the pump becoming too stiff to actuate smoothly and accurately.

The resilient member 15 is positioned between the lip 13 and theretaining portion 16 of the piston head 10. As such, the resilientmember is compressed against the retaining portion 16 when the lip 13 ispushed back, and this can hold the resilient member 15 in place.However, it can be preferable to further secure the resilient member 15in place, to avoid it working loose during use. For example, theresilient member may be attached to the barrier portion 11 or therestraining member 16 by chemical means such as an adhesive.Alternatively, or in combination with an adhesive, the piston head canbe shaped to mechanically hold the resilient member 15 in place. As canbe seen in FIG. 2, the inside surface of the lip 13 is shaped to have anoverhang 16 which projects radially inwards and above the surfaceimmediately below it. This allows for a resilient member 15 to bepositioned under the overhang 16, and thus secured in place by theoverhang 16 acting as a physical blockage to the resilient member 15moving out of place. This effect is increased as the lip 13 is deformedinwardly, moving the overhang further inwards.

The barrier portion 11 and the retaining portion 16 can be made of aplastics material and preferably for nanopore applications uses aplastics material that exhibits low chemical/plasticiser leaching.Possible plastics include polytetrafluoroethylene (PTFE),ultra-high-molecular-weight polyethylene (UHMWPE), polypropylene (PP),perfluoroalkoxy (PFA) or fluorinated ethylene propylene (FEP).

UHMWPE is a preferable material for forming the barrier portion 11 andresilient member 16 because is exhibits a relatively low amount ofcreep, whilst also being mouldable.

Moulding is a preferred manner of producing the piston head 10, becauseit is allows mass manufacture of substantially identical products.Further, moulding enables the formation of the resilient member 15within the lip 13 in a way that ensures that the resilient member fillsthe available space and is securely positioned (e.g. under anyoverhangs). A moulding process may include first moulding the barrierportion 11/retaining portion 16 as an integrated structure that includesall the features of the lip 13, using a plastics material such asUHMWPE. Thereafter, in a second moulding step, the resilient member 15may be formed by moulding the resilient member 15 into the regionbetween the lip 13 and the retaining portion 16. As such the materialused to form the resilient member (TPE for example) will flow under anyoverhangs 16, for example, before setting in position.

Such a two stage process not only produces a good fit between theresilient member 15 and the rest of the piston head 10, but alsoproduces a good bond between the two sections. The moulding can becarried out as part of two-stage over-moulding process, using differenttools for each moulding step. Alternatively, the bond between the twosections can be further improved by using a two-shot moulding processthat utilises the same tool for both moulding operations. A two-shotmoulding process preferably allows for the formation of the resilientmember 15 without exposing the material of the resilient member 15 onthe barrier surface 12. For example, the material for the resilientmember 15 can be injected into position through the retaining portion 16or through the barrier portion 11 from the piston side (using channelsto allow the material to pass through the barrier portion 11 to behindthe lip 13 at the periphery of the barrier portion 11).

The piston 20 is driven by an actuating assembly 40, and specifically bythe actuating member 41. In one arrangement, the piston 20 is providedwith an engagement section, comprising a slot 25, for engaging with theactuating member 41. As shown in the Figures, this section can beprovided with ribs 23 to support the slot 25 and to ensure that the slotremains rigid, but the slot could alternatively be provided in a solidsection of the piston 20.

The slot 25 has two substantially parallel and flat sides. The actuatingmember 41 also has two substantially parallel and flat sides, having adouble-D cross-sectional shape (i.e. two flat sides opposite each otherand two outwardly convex curved sides opposite each other) as visible inFIG. 4 b. When the flat sides of the actuating member 41 are parallelwith the flat sides of slot 25, the actuating member 41 can slide intothe slot 25. Once in position in the slot 25, turning the actuator rod41 will then turn the piston 20 assembly via the flats.

In practice, a fluidics circuit may involve several fluids and requireseveral pumps. By using pump assemblies 1, the circuit can be arrangedwith the slots of all the pumps facing in the same direction, to alloweasy connection to (and subsequent disconnection from) actuating membersby relative motion of the pumps towards the actuating members 41 in adirection substantially perpendicular to the direction in which thepiston 20 travels along the barrel 30. That is, the pumps can be engagedby the actuating members 41 in a sideways fashion. This avoids the need,for example, for the provision of any mechanism to initiate engagementin the direction of piston travel. This further reduces the height (inthe arrangement of the Figures) that the system occupies. Such anarrangement provides space saving advantages whilst being relativelyeasy to construct, by providing the hollow plunger. Alternatively, theactuator 41 could be hollow, or have branched sections from the mainactuator drive shaft, so as to engage with the outer surface of thepiston 20 (e.g. by providing an actuating member 41 that slots overand/or around the piston). In this arrangement, the outer surface of thepiston can be provided with structural features, such as flat surfaces,to allow engagement with the actuator 41 so that the actuator 41 canturn the piston 20. As this piston is turned, it can rise upthrough/within the actuator 41. Such an arrangement can maintain thespace-saving advantages of the arrangement shown in the Figures. Thisarrangement may be preferable, for example, if the pump volume is smallenough that the arrangement shown in the Figures would result in anactuator 41 that was insufficiently strong. That is, if the space withinthe plunger became so small that an actuator 41 of a particular desiredmaterial became too thin and began to flex and/or twist itself ratherthan drive piston 20. In that case, the actuator could be providedoutside the piston 20, allowing the actuator to be thickened andstrengthened whilst maintaining the small pump volume.

Another space saving feature is the provision of a hollow space withinthe plunger 21. This allows for the piston 20 to rise around theactuating member 41 as the piston 20 is withdrawn. That is, there is noneed to withdraw the actuating member 41 at the same time as withdrawingthe piston 20, because the actuating member can extend into the hollowplunger 21. As a result, there is no need to provide any mechanism toenable the withdrawing of the actuating member. The alternative, ofmoving the actuating member 41 with the piston 20 would require extramechanisms (to enable the motion) that would take up extra space.Therefore, once again, the described arrangement assists in reducing theheight of the system.

The longitudinally stationary nature of the actuating member 41 alsoallows for the motor 60 to be coupled to the actuating member 41 via aworm gear 50. Further the motor 60 can be provided to produce arotational driving with an axis of rotation substantially perpendicularto the eventual direction of travel of the piston 20 with respect to thebarrel 30, as discussed in more detail below. As a result, the motor canbe positioned (e.g. in the arrangement of FIG. 1) to the side of theactuating mechanism 40 rather than in a conventional position whichwould linearly interpose an actuating mechanism between a motor and apiston.

To operate the pump system various motors and control systems could beused. In the case of pumping for fluidic and nanopore applications astepper motor system can be preferable. This is because stepper motorsgive a high torque output at low speeds with high positionalrepeatability. Use of a stepper motor therefore allows good control whenpumping at slow rates. Stepper motors are also inexpensive compared withother motion control systems, due to there being no required feedback tothe motion controller. Low cost is important when multiple motors persystem are required, as in the case where there are multiple fluids tocontrol in a nanopore application.

When using a stepper motor in the pump system, the lowest output ratethat can be provided by the pump is also determined by the motorcontroller. Controllers are usually limited by how many steps they canmove per time interval, for example 1 step/s. Therefore to help achievevery low pumping speeds it is more preferable to use a stepper motorthat has a high number of steps per revolution and a controller that hasmicro stepping capability. Micro stepping capability allows thecontroller to move a set number of smaller steps for each motor step.

Size constraints for the motor 60 can also be a consideration in fluidicand nanopore applications. This makes it preferable to use a steppermotor selected with a high power to size ratio.

An example of a motor that could be used as motor 60 is the FaulhaberStepper Motor AM2224-AV-4.8, which has an outside diameter of 22 mm, aholding torque of 26 mNm and 24 steps per revolution (or 15° per step).Of course, alternative motors of similar specifications can also beused. Such a motor can be used in combination with a controller such asthe Allegro A3987 DMOS Micro Stepping Driver, which has the capabilityto move the motor 16 micro-steps per step. In combination, this gives atotal of 384 micro-steps per revolution (or 0.94° per micro-step) andallows a low speed of 1 micro-step per second. The small stepping speedand low change of angle per micro-step translates into fine control ofthe pump output speed.

The provision of the worm gear 50, which drives the gear of theactuating mechanism 40, also allows for a suitable gearing ratio to beselected for the desired operation. As a result, for example, it ispossible to provide very fine control of the pump position by providinga gearing ratio that translates many turns of the worm gear 50 into fewturns of the gear of the actuating assembly 40. For example, a range ofgearing ratios from 1:1 to 50:1 could be appropriate for fluidics andnanopore applications. In addition, the pitch of the screw threadbetween the piston sheath 22 and the barrel 40 can also be varied toaffect how much rotation of the piston is required to produce a certainamount of longitudinal motion. In a particular preferred arrangements,the Faulhaber Stepper Motor AM2224-AV-4.8 is used with the Allegro A3987DMOS Micro Stepping Driver, in combination with a gearing ratio of 35:1,a screw thread pitched to produce 1 mm longitudinal movement perrevolution and a barrel width of 11 mm. This allows for the pump to becontrolled to provide flow rates across a range of from 0.1 μl/s to 100μl/s.

An example of the operation of the pump assembly 1 is discussed below.The skilled reader will understand that this particular method ofoperation is not limiting upon the invention.

The pump barrel 30 can be integrated with a fluidics circuit, with afluid inlet/outlet 31 from the barrel 30 connecting to a flow path inthe fluidics circuit, as shown in the Figures. However, in alternativedesigns, separate inlets and outlets could be provided (with non-returnvalves to prevent flow in the wrong direction). When decoupled from theactuating mechanism 40, the piston 20 can be provided screwed onto thebarrel until the lugs 24,34 come into contact with each other. In thisstate, the piston plunger 21 and head 10 are advanced as far as possiblein the barrel 30, thereby minimising the volume of fluid in the barrel30 (preferably so that the barrel 30 is empty of fluid).

The pump barrel/piston combination can be engaged with a driving member41. The driving member 41 may be part of a larger mechanism or machine.The machine may be configured to provide the driving member in aparticular (rotational) orientation, so that the flat sides of thedriving member 41 are arranged at a particular position to allow theslot 25 of piston 21 to slide around the base of the driving member 41.The piston 21 can slide around the driving member 41 until the drivingmember 41 is positioned in the slot 25, so that an axis of rotation ofthe driving member is substantially coincident with an axis of rotationof the piston 20.

Once the pump barrel/piston combination is engaged with the drivingmember 41, the pump assembly 1 is ready for operation. The motor 60,arranged with its rotational axis substantially perpendicular to thedirection of longitudinal travel of the piston 20 along the barrel 30,can be operated to produce a rotational driving force for the worm gear50. The worm gear 50 is coupled to the actuating assembly 40 via a gear.The gear is positioned at the opposite end of the actuating member 41 tothe end of the actuating member 41 that fits into slot 25 of the piston20.

The rotation of the worm gear 40 causes the actuating assembly gear torotate, and therefore produces a rotational motion of the actuatingmember 41, having an axis of rotation that is substantiallyperpendicular to the axis of rotation of the worm gear 50.

As mentioned above, the slot 25 of the piston is positioned around theactuating member 41, so the rotation of the actuating member causes arotational force to be applied piston 20.

If the rotational force is applied to the piston in a direction thaturges the lugs 24,34 together, the piston 20 will not move because it isalready rotationally advanced as far as it can in that direction.Optionally, the assembly 1 can be provided with a feedback system todetect the non-rotation of the piston 20 and stop (or reverse) the motor60. Alternatively, a mechanism may be employed to keep track of therotational position of the piston to avoid the piston 20 being urgedpast its most advanced point.

If the rotational force is applied to the piston in a direction thaturges the lugs 24,34 apart (i.e. in the direction which will withdrawthe plunger 21 and head 10 within the barrel 30), the piston 20 is freeto rotate along the complementary threads of the sheath 22 and barrel30. As such, the rotational force applied to the piston 20 via the slot25 and the actuating member 41 causes rotation of piston 20 that istranslated into longitudinal motion (i.e. motion along the axis ofrotation) by the threaded surfaces.

The longitudinal motion results in the plunger 21 and head 10 beingwithdrawn within the barrel 30. As previously mentioned, the head 10 canbe connected to the plunger 21 in a manner that allows rotation of thehead 10 relative the piston 20. If so, the head 10 may move within thebarrel so as to maintain its rotational orientation with respect to thebarrel 30 (due to the friction between the barrel 30 and the head 10),and rotate with respect to the piston 20/plunger 21.

If the opening 31 in the barrel 30 is connected to a fluid supply, thefluid will be drawn into the barrel as the plunger 21 and head 10 arewithdrawn. This is because the head 10 provides a seal across the barrel30 that prevents any fluid (e.g. air) entering the space vacated in thebarrel from the plunger side of the head 10, and so the suction pressuregenerated by withdrawing the head draws fluid in through the opening 31.

The longitudinal motion also results in a change in the relativeposition of the piston 20 to the actuating member 41. That is, as thepiston 20 and the actuating member 41 rotate together, the longitudinalmotion of the piston 20 causes the piston to move along the actuatingmember 41 (i.e. move upwardly in the arrangement of FIG. 1). This isenabled by the provision of a hollow space within the plunger 21, intowhich the actuating member 41 can extend through the slot 25. Therefore,as the piston 20 rotates it travels along the actuating member 41,accepting the actuating member 41 further into the hollow plunger 21.

As the piston 20 moves along the actuating member 41, the actuatingmember 41 will begin to extend beyond the slot 25, and so it does notremain possible to disengage the piston 20 from the actuating member 41by lateral motion (i.e. motion perpendicular to the rotation axis of thepiston 20). Therefore, the pump piston/barrel can become locked into themachine housing the actuating mechanism 40 until the piston 20 isreturned to its original position. When the piston is advanced withinthe barrel as shown in FIG. 3 a, the driving member may be disengagedfrom slot 25. This allows for the removal of the barrel and piston thathave been contaminated with fluid sample and the subsequent replacementof a new barrel and piston without having to move the driving memberlongitudinally. This also enables the other components of the pump suchas the drive and motor to be reused. A cartridge 90, for use with ananalysis apparatus, comprising a plurality of pumps, amongst otherfeatures, may be provided as illustrated in FIG. 9 (in which the pistons20 are visible, covering the various barrel portions 30). The entirecartridge may thus be removed and replaced from a surrounding housing orbody that contains the driving members 41 and the associated drivemechanisms.

Once sufficient fluid has been drawn into the barrel 30, the motor 60can be halted. The fluid will be held in the barrel 30 until motion ofthe motor 60 is re-started. The motor 60 can be re-started in theopposite direction to its previous motion, in order advance the plunger21 and head 10 within the barrel 30 and force the fluid out of theopening 31. This may be desirable, for example, if the fluids circuit 31can be reconfigured after fluid has been stored in the barrel 30, toprovide a different flow path to the opening 31, along which it isdesirable to provide the fluid.

Because the pump assembly 1 translates the rotational driving force intoa longitudinal motion of the piston, fine control of the amount of howfluid is expelled (or, indeed, drawn in) through opening 31 is possible.Therefore, the motor 60 can be restarted to provide, for example, aknown number of turns of the worm screw 50, which will translate into acertain (known) longitudinal displacement of the piston 20. If thedimensions of the barrel 30 are known, the volume of fluid displaced(and forced into the fluidics circuit) will also be known. Therefore,the pump assembly 1 can be used to provide metered amounts of fluids. Inan alternative operation, by controlling the speed at which the motor 60turns the worm gear 50, and thus the piston 20, the pump assembly 1 canbe used to provide a specific flow rate of fluid through the opening 31.In practice, it can be desirable to control both the flow rate of fluidand the total amount of fluid delivered simultaneously, and the pumpassembly 1 makes this possible.

The fluid in the barrel 30 may be expelled all at once, or inincrements. The fluid may also be replenished before it is all expelled(by using the motor to withdraw the piston 20 further). It is alsopossible for the fluid in the barrel 30 to be changed if the fluidicsconnected to the opening 31 can be changed. For example, a first fluidmay be drawn into the barrel 30 and subsequently expelled, the fluidicscircuit connected to the opening 31 could be reconfigured and a newfluid supply connected to be drawn in.

Once the piston 20 has been advanced back to the point at which the lugs24,34 meet, it is possible to disengage the pump barrel/pistoncombination from the actuating assembly 40.

As will be understood from the foregoing description, the pump assembly1 allows for the accurate provision of amounts of fluid, whilst alsomaintaining a low pump profile, by employing a design that reduces therequired longitudinal space for providing actuation and by translatingthe rotational motion of the piston 20 into a longitudinal motion by useof the screw thread. The construction also allows for the pump parts tobe produced cheaply, without compromising the accuracy of fluiddelivery, which in turn provides the possibility of the pump being useddisposably.

In practice, the pump and drive train shown in the Figures will becontained within a casing, as part of a system such as a fluidics ornanopore system. The construction of the pump and actuator 41 allows forthe actuator 41 to be mounted in the casing so that it is rotatable, butotherwise held stationary, with respect to the casing. That is, theactuator 41 is held translationally stationary. As a result, there is noneed to provide any extra space in the casing to allow for translationalmotion of the actuator 41 during pumping. Instead, as the piston isdriven by the rotational motion of the actuator 41, the actuator 41remains in the same translational position with respect to the casing.The barrel 30 can also be held stationary within the casing, allowingeasy connection to any fluidic system as required.

The system can be arranged so that the pump can be introduced within thecasing, on a cartridge for example. In such a system, the loading of thecartridge may bring the pump on the cartridge into engagement with theactuating member.

In such systems, it may be preferable to save space in the system byreducing the width or height of the opening in the casing, through whichthe cartridge is inserted, as far as possible. In that case, it may bepreferable for the pump on the cartridge to be introduced in an ‘empty’configuration with the plunger advanced as far into the barrel aspossible. In that case the pump will present the lowest profile on thecartridge. As cartridge profile will depend upon cartridge components,including the pump, reducing the profile of the pump contributes toproviding a lower overall cartridge profile. A reduction in cartridgeprofile allows a corresponding reduction in the size of the openingthrough which the cartridge is inserted into the casing, and so cancontribute to a reduction in the overall system size. Once the cartridgehas been inserted, and the pump is brought into engagement with theactuating member, the pump can be raised around the actuating member andoperated as discussed above.

In other cases, it may be preferable to insert the cartridge with thepump pre-filled. In those cases, the pump will present a larger profilebecause the piston will be withdrawn out of the pump and so projectfurther ‘up’ (in the sense of the accompanying Figures). In that case alarger slot for the cartridge would be required.

Although the system has been described above with respect to a singlepump on a cartridge, some systems may utilise a plurality of pumps thatare all provided on a single cartridge.

The present invention has been described above with reference tospecific embodiments. It will be understood that the above descriptiondoes not limit the present invention, which is defined in the appendedclaims.

1. A pump comprising: a barrel for holding fluid; and a piston fordrawing fluid into the barrel and driving fluid out of the barrel,wherein the piston comprises a plunger configured to move within thebarrel and a sheath configured to move around an outer surface of thebarrel; wherein an inner surface of the sheath and the outer surface ofthe barrel have complementary screw threads so that, in use, rotatingthe piston causes the piston to travel along the barrel.
 2. The pumpaccording to claim 1, wherein the plunger is hollow.
 3. The pumpaccording to claim 2, wherein the piston comprises an engagement sectionfor engaging with a driving member and enabling the driver to turn thepiston.
 4. The pump according to claim 3, wherein the engagement sectioncomprises an opening into the hollow plunger.
 5. The pump according toclaim 3, wherein the engagement section comprises a slot for engaging adriving member by relative motion between the pump and the drivingmember in a direction substantially perpendicular to the direction oftravel of the piston along the barrel.
 6. The pump according to claim 4,further comprising the driving member.
 7. The pump according to claim 6wherein, in use, the driving member is held translationally stationarywith respect to the piston and barrel whilst the piston is movedrelative to the barrel.
 8. The pump according to claim 6 wherein thedriving member is disengageable from the engagement section.
 9. The pumpaccording to claim 6, wherein the driving member has two flat andsubstantially parallel sides for engaging the engagement section. 10.The pump according to claim 6, wherein the pump is configured such that,in use, the driving member extends within the hollow plunger as thepiston travels along the barrel.
 11. The pump according to claim 6,wherein the driving member, in use, moves rotationally with respect tothe barrel to drive the piston within the barrel.
 12. The pump accordingto claim 6 further comprising a gear arranged to rotate the drivingmember, the gear being arranged to rotate with an axis of rotationsubstantially perpendicular to the axis of rotation of the drivingmember.
 13. The pump according to claim 12 wherein the gear is a wormgear.
 14. The pump according to claim 6, further comprising a steppermotor arranged to drive the driving member.
 15. The pump according toclaim 1, further comprising a piston head for forming a seal against aninner surface of the barrel, wherein the piston head is connected to theplunger of the piston so that the piston head is free to rotate withrespect to the plunger or the barrel.
 16. The pump according to claim 1,wherein the pump is configured to resist rotation of piston relative thebarrel at a predetermined position.
 17. The pump according to claim 1,wherein the sheath is provided with a lug for resisting rotation of thepiston relative to the barrel when the lug is brought into contact withanother portion of the pump.
 18. The pump according to claim 1, furthercomprising a driving member that engages the outer surface of thepiston.
 19. (canceled)
 20. (canceled)
 21. (canceled)
 22. (canceled) 23.(canceled)
 24. An analysis apparatus comprising a body and a cartridgeattachable to the body, wherein the cartridge comprises a pump accordingto claim 5 and wherein the body comprises a driving member for engagingwith the pump by relative motion between the pump and the driving memberin a direction substantially perpendicular to the direction of travel ofthe piston along the barrel.
 25. An analysis apparatus according toclaim 24 wherein the cartridge comprises a plurality of pumps and thebody comprises a plurality of respective driving members.
 26. Ananalysis apparatus according to claim 24 wherein the body furthercomprises a gear for rotating the driving member and a stepper motor fordriving the driving member.
 27. (canceled)
 28. (canceled)
 29. (canceled)30. (canceled)